The present invention relates to a displacement control apparatus for controlling the displacement of a variable displacement compressor.
A typical compressor used for a vehicle air-conditioning system is connected to an internal combustion engine of a vehicle, which is an external drive source, via a clutch mechanism such as an electromagnetic clutch. When refrigeration is not needed, the power transmission is stopped by disengaging the electromagnetic clutch. The compressor is stopped accordingly.
Engaging and disengaging the electromagnetic clutch causes shock. The shock lowers the driving performance of the vehicle. Therefore, a clutchless type compressor, which does not have a clutch, has been proposed. A variable displacement type compressor is used for the clutchless type compressor. When refrigeration is not needed, the variable displacement type compressor minimizes the displacement of the compressor, thereby stopping refrigeration.
Changing the pressure in a crank chamber, which accommodates a drive plate, changes the difference between the pressure in the crank chamber and the pressure in the cylinder bores. This changes the inclination angle of the drive plate. When the inclination angle of the drive plate is zero, pistons do not reciprocate. That is, refrigerant is not compressed. In this state, there is no difference between the pressure in the crank chamber and the pressure in the cylinder bores. Thus, the inclination angle of the drive plate cannot be increased. Therefore, the displacement of the variable displacement type compressor cannot be set to zero. As a result, unnecessary compression is performed and the fuel economy of the internal combustion engine deteriorates.
The objective of the present invention is to provide a displacement control apparatus that sets the minimum displacement of a variable displacement compressor to zero.
To attain the above object, the present invention provides a displacement control apparatus for a variable displacement compressor used in a refrigerant circuit of an air conditioner. The compressor is driven by an internal combustion engine. The compressor has an inclining drive plate and a piston, which is reciprocated by the drive plate. The stroke of the piston is changed in accordance with the inclination angle of the drive plate. The displacement of the compressor is changed between a minimum displacement and a maximum displacement in accordance with the stroke of the piston. The apparatus comprises an actuator connected to the drive plate. The actuator is actuated by the exhaust pressure or the intake pressure from the engine. A controller changes the inclination angle of the drive plate by actuating the actuator.
The present invention also provides a method for controlling a displacement control apparatus for a variable displacement compressor used in a refrigerant circuit of an air conditioner. The compressor is driven by an internal combustion engine. The compressor has an inclining drive plate and a piston, which is reciprocated by the drive plate. The stroke of the piston is changed in accordance with the inclination angle of the drive plate. The displacement of the compressor is changed between a minimum displacement and a maximum displacement in accordance with the stroke of the piston. The method includes changing the inclination angle of the drive plate by applying a force to the drive plate. The force is created by exhaust pressure or intake pressure from the engine.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.